Materials Chemistry and Crystal Growth

Materials chemistry and crystal growth are seen as closely related activities because the assessment and implementation of numerous physical properties are based on single crystals and epitaxial layers. The idea of a materials synthesis directed toward the investigation and application of physical solid-state properties is outlined by three examples: i) the supramolecular synthesis of polar molecular crystals, ii) a quest for optical materials for short wavelength generation, and iii) crystal growth and epitaxy of fluoride laser materials

Response of Large Diameter Offshore Wind Turbine Monopile Foundations to Extreme Event Loading Expected at U.S. Atlantic Coast Wind Energy Areas

Extra-tropical (ETC) and tropical cyclones (TC) pose potential risks to offshore wind farms along the U.S. Atlantic coast, where the offshore wind energy industry is gaining momentum. This research aims to evaluate the stability of large diameter offshore wind turbine monopile foundations under these extreme conditions using the governing industry practice in IEC 61400-3-1. To quantify the risk at U.S. Atlantic coast wind energy areas (WEAs), the ETC and TC impact frequency and intensity are identified using the NHC Historical Hurricane Tracks Archive. Numerical simulations in Plaxis 3D are performed on foundations ranging from 8 to 12 meters in diameter embedded in medium dense sand. Storm conditions correspond to Saffir-Simpson category 1 through 4 wind speeds and associated metocean criteria. A database of foundation mudline rotation and deflection is presented for each storm intensity, turbine size and water depth. The anticipated monopile foundation stability is then predicted for each WEA

Superconducting phase formation in random neck syntheses: a study of the Y-Ba-Cu-O system by magneto-optics and magnetometry

Magneto-optical imaging and magnetization measurements were applied to investigate local formation of superconducting phase effected by a random neck synthesis in Y-Ba-Cu-O system. Polished pellets of strongly inhomogeneous ceramic samples show clearly the appearance of superconducting material in the intergrain zones of binary primary particles reacted under different conditions. Susceptibility measurements allows evaluation of superconducting critical temperature, which turned out to be close to that of optimally doped YBCO.Comment: 6 pages, 11 figure

Polarity formation by a higher order interaction Markov-like chain

Vector property generation is discussed for chain growth by higher order interactions. Because of a deterministic property evolution a state space approach was used. Although not strictly Markovian, the system shows ergodic properties and convergence for a large number of attachment steps. For reasonable interaction energies attributed to increasing order, the main extra contribution to polarity formation results from interactions up to next nearest neighbours. Nonlinear equations up to third order were solved by an iterative procedur

Czochralski growth and spectroscopic investigations of Yb3+, La3+:Na2SO4(I) and Nd3+:Na2SO4(I)

Ln3+-stabilized Na2SO4 (phase I) single crystals were grown by the Czochralski method. Differential thermal analysis revealed the influence of the ionic radius of Ln3+ on the stabilization of Na2SO4(I). Distribution coefficients (∼0.8-1.1) were measured by the inductively coupled plasma optical emission spectroscopy method and x-ray fluorescence spectroscopy. Spectroscopic investigations yielded absorption cross sections of 0.6 × 10−20 cm2 (π-polarized, 928.5 nm) and 1.5 × 10−20 cm2 (π-polarized, 797.3 nm) for Yb3+, La3+:Na2SO4 and Nd3+:Na2SO4, respectively. Crystal growth of Gd3+-stabilized Na2SO4(I) provides an interesting new material for stimulated Raman scattering experiment

Universality behaviour for polarity formation in channel-type inclusion compounds

A statistical investigation based on a Markov chain theory of polarity formation applied to channel-type inclusion compounds loaded with both dipolar A-π-D and non-polar N-π-N (N: A or D) guests is presented. The key parameters effecting polarity formation are identified and their effects are explored. A number of paradoxes are set out and an attempt to explain the mechanisms behind them is made: dependence of macroscopic polarity on orientational selectivity induced by intermolecular interactions, tuning of polarity through (i) the concentration of non-polar guest and (ii) growth temperatur

Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics

A single-sample synthesis concept based on multi-element ceramic samples can produce a variety of local products. When applied to cuprate superconductors (SC), statistical modelling predicts the occurrence of possible compounds in a concentration range of about 50 ppm. In samples with such low concentrations, determining which compositions are superconducting is a challenging task and requires local probes or separation techniques. Here, we report results from samples with seven components: BaO2, CaCO3, SrCO3, La2O3, PbCO3, ZrO2 and CuO oxides and carbonates, starting from different grain sizes. The reacted ceramics show different phases, particular grain growth, as well as variations in homogeneity and superconducting properties. High-Tc superconductivity up to 118 K was found. Powder x-ray diffraction (XRD) in combination with energy-dispersive spectroscopy (EDS), scanning transmission electron microscopy (STEM) can assign Pb1223 and (Sr,Ca,Ba)0.7-1.0CuO2 phases in inhomogeneous samples milled with 10 mm ball sizes. Rather uniform samples featuring strong grain growth were obtained with 3 mm ball sizes, resulting in Tc =70 K superconductivity of the La(Ba,Ca)2Cu3Ox based phase. Scanning SQUID microscopy (SSM) establishes locally formed superconducting areas at a level of a few microns in inhomogeneous superconducting particles captured by a magnetic separation technique. The present results demonstrate a new synthetic approach for attaining high-Tc superconductivity in compounds without Bi, Tl, Hg, or the need for high-pressure synthesis

Symmetry and the polar state of condensed molecular matter

Polar molecular crystals seem to contradict a quantum mechanical statement, according to which no stationary state of a system features a permanent electrical polarization. By stationary we understand here an ensemble for which thermal averaging applies. In the language of statistical mechanics we have thus to ask for the thermal expectation value of the polarization in molecular crystals. Nucleation aggregates and growing crystal surfaces can provide a single degree of freedom for polar molecules required to average the polarization. By means of group theoretical reasoning and Monte Carlo simulations we show that such systems thermalize into a bi-polar state featuring zero bulk polarity. A two domain, i.e. bipolar state is obtained because boundaries are setting up opposing effective electrical fields. Described phenomena can be understood as a process of partial ergodicity-restoring. Experimentally, a bi-polar state of molecular crystals was demonstrated using phase sensitive second harmonic generation and scanning pyroelectric microscop

Superconductivity and non-metallicity induced by doping the topological insulators Bi2Se3 and Bi2Te3

We show that by Ca-doping the Bi2Se3 topological insulator, the Fermi level can be fine tuned to fall inside the band gap and therefore suppress the bulk conductivity. Non-metallic Bi2Se3 crystals are obtained. On the other hand, the Bi2Se3 topological insulator can also be induced to become a bulk superconductor, with Tc ~ 3.8 K, by copper intercalation in the van der Waals gaps between the Bi2Se3 layers. Likewise, an as-grown crystal of metallic Bi2Te3 can be turned into a non-metallic crystal by slight variation of the Te content. The Bi2Te3 topological insulator shows small amounts of superconductivity with Tc ~ 5.5 K when reacted with Pd to form materials of the type PdxBi2Te3